The Optical Properties Of ZnO Nanostructure

ZnO is a wide-gap semiconductor(Eg=3.37eV) with a high exciton binding energy of 60meV in favor of fabrication of UV light-emitting devices and semiconductor laser.Various ZnO nanostructures have been successfully synthesized due to its particular structure.Because of size effect,ZnO nanostructures have potential applications in nano-optoelectronic devices and gas sensors.It is necessary to investigate the optical properties of ZnO in order to improve the performances of ZnO-based devices and further explore its applications.In this thesis,ZnO nanocrystal films have been prepared by pulse laser deposition(PLD) and characterized to find out the effect of its morphology and composition on optical properties.In particular,the emission mechanism at low temperature has been explored.Moreover,ZnO nanodot has been prepared by chemical vapor deposition and characterized for its optical properties.In this work,the results are listed as follow:1.ZnO nanocrystal films have been grown by PLD on the In₂O₃ template obtained on the Si (111) wafer in advance,and then ZnO nanodots have been deposited on the films by CVD.2.Based on the characterization of optical properties of ZnO nanocrystal films,emission mechanism has been analyzed.According to temperature-dependent PL spectra,a strong emission at 3.372eV at 15K is found.After coating a Al₂O₃ layer,surface exciton is excluded as origin of the emission at 3.372eV.The emission in samples grown at different temperature show activation energies of several meV..With the temperature increase,free exciton emission is gradually present,indicating that the emission peak at 3.372eV is reasonably assigned to localized exciton.3.The drastic change in morphology of ZnO films and the peak energy and intensity of emission at low temperature are found after annealing.4.Two near band edge emissions that are rarely reported has been observed in ZnO nanodots. The emission from ZnO nanodots is attributed to deep acceptors with energy level of～120 meV according to temperature-dependent PL spectra.It is a complex in optical properties that the ZnO nanocrystal prepared by different methods shows a strongly discrepancy in emission and corresponding mechanism in spite of a similar morphology.The optical properties in ZnO nanostructures are profoundly researched by other assisted characterization besides PL due to some currently unresolved issues.